Algebra
# Roots of Unity

Given \(z^2+z+1=0,\) find the value of

\[\left(z+\dfrac{1}{z} \right)^2+\left(z^2+\dfrac{1}{z^2}\right)^2+\left(z^3+\dfrac{1}{z^3} \right)^2+\cdots+\left(z^{21}+\dfrac{1}{z^{21}}\right)^2.\]

\[ \large{\dfrac{31-2\delta_{1}}{1-2\delta_{1}} +\dfrac{31-2\delta_{2}}{1-2\delta_{2}}+\dfrac{31-2\delta_{3}}{1-2\delta_{3}}} \]

If \(\large{1,\delta_{1},\delta_{2},\delta_{3}}\) are distinct fourth roots of unity, then evaluate the expression above.

If \(w=e^{2\pi{i}/5}\), find \[\sum_{k=1}^{4}\frac{1}{1+w^k+w^{2k}}\]

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